It is well known that overall fuel efficiency in a multiple-cylinder internal combustion engine can be increased by deactivation of the intake and/or exhaust valves for particular cylinders under certain engine load conditions. A known approach to providing selective valve deactivation in a push rod engine is to equip the lifters for the valves to be deactivated with means whereby the lifters are rendered incapable of transferring the cyclic motion of engine cams into reciprocal motion of the associated pushrods and valves. Typically, a deactivation lifter in a push rod engine includes concentric inner and outer portions which are mechanically responsive to the pushrod and to the cam lobe, respectively, and which may be selectively latched to each other.
When latched, the inner body member is rigidly supported in an extended position relative to the outer body member. A pre-determined engine oil pressure applied to the latch assembly moves latch members to an unlatched position. The unlatched inner body member collapses into the outer body member from its latched, extended position. The resulting lost motion prevents transmission of the reciprocal motion of the cam follower to the engine valve.
In push rod type valve trains, this type of valve deactivator assembly is incorporated into the cam follower so that the lost motion prevents the reciprocal motion of the cam follower from being delivered to the push rod. In overhead cam (“OHC”) engines of the type utilizing an end pivot rocker arm, the pivot point for one end of the rocker arm is typically a hydraulic lash adjuster (“HLA”), with the opposite end of the rocker arm being in engagement with the valve stem. In the OHC valve train, the valve deactivator assembly is configured to produce lost motion at the HLA pivot point. Lost motion at the HLA pivot point prevents valve actuation by preventing force delivery to the engine valve stem.
Prior art valve deactivator assemblies have typically employed one or more spring-biased latch members that are responsive to fluid pressure to move from a radially outward latched position to a radially inward unlatched position. In these prior art assemblies, the latch member is itself acted on by the pressurized fluid and also engages a latching surface in the outer body member to support the inner body member in its extended latched position relative to the outer body member. In this type of prior art deactivator assembly, the latch members function as both hydraulically responsive members and reciprocating mechanical latches. The need to configure latch members to perform both of these functions has compromised and complicated latch assembly design.
U.S. Pat. Nos. 6,321,704 and 6,578,535 discuss the shortcomings of prior valve deactivator assemblies employing diametrically opposed latch members in the form of cylindrical pins. The pins are radially outwardly biased toward a latched position by a compressed spring. In their latched position, the locking pins are positioned in a groove and exposed to an engine oil gallery. Engine oil pressure applied to the outer ends of the pins compresses the spring, moving the pins radially inwardly to an unlatched position. These latch members have relatively small load-bearing latching surfaces, resulting in force concentrations and wear problems. The '704 and '535 patents address force concentrations at the pin/outer body interface by providing each pin with a flat surface complementary to a latching surface on the outer body member. The latching assemblies are then required to maintain the locking pins in a particular rotational position to maintain these flat surfaces parallel to the corresponding latching surface of the outer body member.
There is a need in the art for a reliable valve deactivator assembly of simplified design that provides a reliable and robust latching mechanism.